The present invention relates generally to heat storage systems, and more specifically to a very high capacity heat sink suitable for storing waste heat from a space-based burst power suppy.
Space-based burst power supplies will produce multimegawatt outputs for several hundreds of seconds. State of the art radiators to dissipate the waste heat from those power supplies are too heavy for use in space. Open cycle systems are more lightweight but, among other problems, the thrust from their exhaust plumes will require elaborate thrust cancellation devices to work in space. Closed cycle systems that temporarily store the waste heat from a burst power supply and slowly release the stored thermal energy during an off period are a possible solution. That solution requires a heat sink material able to absorb very large amounts of thermal energy. Lithium hydride is a good candidate for use as the heat sink material, having both a very high heat capacity and a very high heat of fusion. Co-pending application Ser. No. 24,447 by Kennel, one of the applicants for the present invention, demonstrates the successful use of lithium hydride in a closed cycle space-based nuclear reactor. The thermal energy stored in the lithium hydride during an on period is released through a radiator during an off period.
Unfortunately, lithium hydride conducts heat poorly and expands greatly upon melting, making high heat transfer rates and containment difficult to achieve. Further, containment of lithium hydride requires a hydrogen overpressure, necessitating containment of both free hydrogen and free lithium. Free hydrogen is generally difficult to contain. It will embrittle, corrode, or otherwise damage many materials, especially materials, such as niobium, that are particularly compatible with lithium.
Stainless steel or titanium, as shown in Kennel's nuclear reactor, will contain free hydrogen, but must be made relatively thick to do so, adding unwanted weight.
It is, therefore, a principal object of the present invention to provide a heat storage system using lithium hydride which both safely contains and provides a high rate of heat transfer to and from the lithium hydride.
It is another object of the present invention to provide a heat storage system using lithium hydride that is light in weight.